ZyXEL Communications ISG50-ISDN Application Note page 101

Assign the priority to each extension. The priority represents which extension the incoming calls are routed to first.
1 is the highest priority while 5 is the lowest priority.
When an incoming call comes in this hunt group, this call will be routed to priority 1 first along with the ring strategy.
If no extensions with priority 1 are available, the call will then be routed to extensions with priority 2.
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